Radio apparatus



March 1951 R. H. HAGOPIAN RADIO APPARATUS Filed Dec. 7, 1948 V INVENTORRichard H; Hugopion.

Patented Mar. 20, 1951 RADIO APPARATUS Richard H. Hagopian, Baltimore,Md., assignor to Westinghouse Electric Corporation, East Pittsburgh,Pa., a corporation of Pennsylvania Application December 7, 1948, SerialNo. 64,013

18 Claims.

This invention relates to automatic voltage controls for radio ferquencygenerators, and relates more particularly to controls for maintainingconstant the radio frequency voltages of generators having variableloads, such as those used in induction and dielectric heating systems.

In systems using radio frequency generators such, for example, asinduction and dielectric heating systems, it is desirable to maintain aconstant power density in the load regardless of changes in theprojected area of the load. This is especially important in dielectricheating systems using conveyors where large load changes frequentlyoccur.

Load changes cause changes in the radio frequency output voltages of thegenerators. If a generator has been adjusted to supply a predeterminedpower into its load, then if the load is reduced, the radio frequencyvoltage of the generator will increase. By maintaining the radiofrequency voltage of a, generator constant, the power supplied to itsload can be maintained constant.

Prior systems for maintaining the output voltages of radio frequencygenerators constant have used relays which were energized inone'direction upon increases in the radio frequency voltage of thegenerators to actuate contacts for closing circuits for decreasin thevoltages, and which were energized in the opposite direction upondecreases in the radio frequency voltage to actuate contacts for closingcircuits for increasing the voltages. Such system have had thedisadvantages that control over a wide range could be accomplished onlyin steps, and that hunting sometimes occurred. 7

This invention provides a voltage stabilizer which is continuous inaction over a wide range and in which relays are not used.

In one embodiment of this invention, radio frequency current from theoutput circuit of a generator is rectified and used to bias a thyratrontube which supplies a direct current, the average value of which varieswith variations in the radio frequency voltage, to the armature windingof a reversible motor which adjusts the filament voltage of theoscillator tubes of the generator. Current from a constant voltage,direct current, supply source is applied in opposite polarity to thearmature winding. Undesired decreases in the radio frequencyvoltage ofthe generator, caused by increases in its load, cause the thyratron tubeto supply currents to the armature of the motor which are smaller thanthat supplied by the direct current source, causing the motor to beenergized to rotate in a direction to increase the voltage supplied tothe filaments of the oscillator tubes, and to thereby increase the radiofrequency voltage of the generator. Undesired increases in the radiofrequency voltage of the generator, caused by decreases in its load,cause the currents supplied by the thyratron tube to the armature of themotor to be larger than the current supplied by the direct currentsource, causing the motor to be energized to rotate in the oppositedirection to decrease the voltage supplied to the filaments of theoscillator tubes, and to thereby decrease the radio frequency voltage.

An object of the invention is to maintain a constant voltage in theoutput circuit of a radio frequency generator.

Another object of the invention is to provide a voltage stabilizingsystem for a radio frequency generator which will operate over a widerange of voltages. v

Another object of the invention is to provide a voltage stabilizingsystem for a radio frequency generator which will operate withouthunting.

The invention will now be described with reference to the drawing whichis a circuit schematic illustrating one'embodiment of the invention.

The radio frequency generator, the output voltage of which is to bemaintained constant, comprises the push-pull connected oscillator tubes10 having their grids connected together through the inductor I I, thecenter point of which is connected through the resistor I2 to ground.The plates of the tubes are connected together by the tank inductor I 3,the center point of which is connected to the positive terminal of aconventional, plate voltage, supply source I4. The plates of theoscillator tubes are also connected to a load I5 which may be adielectric heating load, an induction heating load, or any other form ofload with which radio frequency generators are used.

The filaments of the oscillator tubes ID are connected together and tothe secondary winding of the filament transformer I6. The primary windinof the transformer has one end connected to one end of the conventionalautotransformer I1, and its other end connected to the slider I8 of theauto-transformer. The autotransformer is connected to a conventionalalternating current source, and its slider I8 is arranged to be adjustedby the rotation of the armature I9 of the electric motor 20 for varyingthe voltage supplied to the filaments of the oscillator tubes.

The plate of one of the oscillator tubes In is connected through theseries connected voltage dividing capacitors 2| and 22 to ground, thejunction point of the capacitors being connected to the plate of thediode rectifier tube 23. The plate of the tube 23 is connected to oneend of the radio frequency choke 24, the other end of which is connectedto one. end of the resistor 25, and

the other end of which terminates in the contact 26. The slider 2'! ofthe resistor 25 is connected to the contact 28. The cathode of the tube23 is connected through the resistor to ground.

The switch 36 which is adapted to contact either the contact 26 or 28;isconnected to "the:

cathode of the thyratron tube 3!, and'through the capacitor 32 toground. The selenium rectifier 29 is shunted across the capacitor 32-The plate of the tube 3i is connected tothe slider 33 of the resistor34, and its grid is connected tothe slider 35 of the resistor 34. Theresistor 34 is shunted across the secondary winding of the transformer3'5, the primary Winding of which is connectedto the alternatin currentsource.

The resistor 34 is tapped at 38, the tap being.

tated'in onedirection by direct current supplied from the tube3l as willbe described.

The ungrounded side of the armature 43 is also connected through theselenium rectifiers43 tothe tap 44 on the'resistor'45, oneend of whichis connected to the grounded side of the armature winding 46, and theother end of which. is con-' nected through the series connectedresistor: 46'

and filter choke 47 to one output side'of the rectifier 48 whichincludes: the fourseleniumrectifiers 43 connected in aiconventionalbridgecircuit, theother-output side of the rectifier'48 being connectedto the grounded end of the resistor 45. The input side of the rectifier48 is :connected to the secondary winding of the transformer 51 theprimary winding of'which is .connected to the alternating currentsource.

The capacitors Hand 52 connected tothe-01%- posite ends of the choke 41and to'ground, are filter condensers. is connected across the resistor45.

The rectifier 48 is a source of constant voltage; direct current, whichsupplies current of opposite polarity to that provided by the'thyratrontube: 3!, to the armature winding of the motor 20;

for causing its armature I9 to rotate in the opposite direction to thatcaused by the'current:

from the thyratron tube as will be described;

The selenium rectifiers 2'9 and 43 provide unidi.-'

rectional current flow in their respective circuits.

In operation, the rectifier tube 23 rectifies radio frequency currentfrom the tank circuit'of the oscillator *tubes, and supplies therectified current through the radiofrequency choke 24 and theresistorr25xand switch 36, to charge the capaci' tor 32 which isconnected to the cathode of the thyratron tube'3l, negatively. The. tube3 lis so biased'from resistor 34 so' that it does not conduct until itscathode becomes sufficiente 1y negative withrespect to its grid as thecharge inthe capacitor 32 increases. At a predeter mined-negative chargein the capacitor, thetube" 3| conducts, and rectified current fromits'plate The voltage regulating tube -53 circuit flows through thearmature winding 40 of the motor 20. Current of opposite polarity fromthe rectifier 48 also flows through the armature winding l9. It isunderstood that, if desired, instead of obtaining the bias for tube 31from resistor 34 a separate fixed bias may be provided for tube 3|.

The time required for the capacitor 32 to charge up to the'firingvoltage of the tube 31 depends upon the equation C (RH-R2) Where C isthe capacity of the capacitor 32 in farads; R1 is the. resistance of theresistor 25 in ohms, and R2 is the resistance of the resistor 30 inohms. Variationcof theradiofrequency current from the radio frequencygenerator supplied to the rectifier tube 23, causes'variation of thecurrent flow through the-resistors 25 and 30 which, in turn, varies thetime required for the capacitor 32 to charge up to the firing voltage ofthe tube 31. The discharge time of the capacitor 32 is, however,-. the.same: at all times.

After each firingof the tube 3!, the capacitor 32- isdischarged.so'thattheztube 3| is blocked by its grid voltage until the.capacitor 32 is again charged tothe firing voltageof the tube, thiscycle being repeated.. In. this way, radio frequency voltageyariationscause) corresponding variations in: theerectifiedccurrent through thetube 3| Although the pulse-of rectified current is the same each time,the average current will depend vupon the time requiredto charge thecapacitor 32.

Assuming that the. radio frequency generator has been adjusted to supplya constant power, which,-iby way. of example may be kilowatts,intotheload .I 5, andthe currentfrom the tube'3l hasbeen adjusted byadjustment of the sliders 33 and'35 alongthe resistor 34-, untilitis-equal to the current of I oppositepolarity from the rectifier 48,thenno :current will flow through the armature winding 40-, and themotor 2il-will not operate.

Now assume that the load on the generator decreases .so thaththe radiofrequency voltage increases. above its normal value. Then the rectifiedradio frequency current from the tube- 23 will charge the capacitor. 32at. afaster rate causing the tube 3 l to conduct at .a correspondingfaster rate, and :to supply an average current to :the armature.winding, it-which is greater than that supplied by therectifier. 48.This will provide-acurrent flow through the armature windingin adirectionto adjust the slider l3 along-the auto-transformer I! fordecreasing the voltagelsuppliedby the transformer It to the filaments ofthe oscillator tubes I0. This-reduction in filament voltage willcausethe tank radio frequency voltage to 2 decrease, and will consequentlycause the power: supplied to the reduced load to .be decreased .tonormal.

When the load on the generator increases, its tank radio frequencyvoltage willdecrease below normal,. causing.the current supplied by thethyratron.tube:3l tothe armature. winding 40 to be less than thatsupplied bythe rectifier 43, so that current will flowxthrough. thearmature winding 40 in a direction to'causeits armature torotate to-movethesliderlBof the auto-transformer to increasethe voltagessupplied bythe transformer l6 to the filaments of the oscillator tubes ID; Thisincreasein: the. filament. voltage of the oscillator tubes will causeanincrease in the radio frequency voltage andaresulting increase in thepower. output. of. the generator.

Thus withan increasein therradio frequency voltage from the generator,the rectified current from the rectifier tube 23 increases and decreasesthe charging time of the capacitor 32. This causes an increase in theaverage rectified current through the thyratron tube 3|, and causescurrent flow through the motor armature winding 40 in a direction tocause the motor to act to decrease the voltage supplied to the filamentsof the oscillator tubes I 0. With a decrease in radio frequency voltage,this process is reversed.

The slider 21 of the resistor 25 and its contact 28 are provided so thatmore than one range of radio frequency voltages may be maintained. Byplacing the switch 36 on the contact 26, 20,000 volts, by way ofexample, may be maintained. By placing the switch 36 on the contact 28and by adjusting the slider 21 along the resistor 25, radio frequencyvoltages of 10,000 volts and lower may be maintained.

I claim as my invention:

1. A voltage stabilizing system for a radio frequency generator,comprising means for varying the voltage of the radio frequency outputcurrent of the generator; a reversible motor for adjusting saidvoltagevarying means; means for rectifying radio frequency current from thegenerator; means utilizing variations in the rectified current forproviding a direct current which varies conformably therewith; a directcurrent source of constant voltage, and means conducting said firstmentioned direct current and conducting current from said direct currentsource in opposite polarity to said motor for energizing same to rotatein one direction when said first mentioned direct current is greaterthan the current from said direct current source, and for energizingsaid motor to rotate in the opposite direction when said first mentioneddirect current is smaller than the current from said direct currentsource.

27 A voltage stabilizing system for a radio frequency generatorincluding an oscillator tube having a filament and a plate; a source ofcurrent for said filament; means including a reversible motor forvarying the voltage supplied by said source to said filament; means forrectifying radio frequency current from the generator; means utilizingvariations in the rectified current for providing a direct current whichvaries conformably therewith; a direct current source of constantvoltage, and means conducting said first mentioned direct current andconducting current from said direct current source in opposite polarityto said motor for energizing same to rotate in one direction when saidfirst mentioned direct current is greater than the current from saiddirect current source, and for energizing said motor to rotate in theopposite direction when said first mentioned direct current is smallerthan the current from said direct current source.

3. A voltage stabilizing system for a radio frequency generator,comprising means for varying the voltage of the radio frequency outputcurrent of the generator; a reversible motor for adjusting said voltagevarying means; a rectifier connected to said generator for rectifyingradio frequency current therefrom; an electron tube; a power supplysource connected through said tube to said motor; means utilizing therectified radio frequency current from said rectifier for impressingupon said tube a potential causing it to conduct and to supply directcurrent from said source to said motor, and a direct current source ofconstant voltage, connected to said motor in polarity opposition to thecurrent from said tube, said motor being energized to rotate in onedirection when the current from said tube is greater than the currentfrom said source, and being energized to rotate in the oppositedirection when the current from said tube is less than the current fromsaid source.

4. A voltage stabilizing system for a radio frequency generator,comprising means for varying the voltage of the radio frequency outputcurrent of the generator; a reversible motor for adjusting said voltagevarying means; a rectifier having an anode; means for supplying radiofrequency current from said generator to said anode; a capacitor havingone side connected to said anode; a gaseous electron tube having a grid,a cathode, and an anode, means connecting the cathode of said tube tothe other side of said capacitor; a power supply source connected tosaid grid and anode of said electron tube and to said motor, saidelectron tube conducting and supplying direct current to said motor whensaid capacitor has been charged to a predetermined voltage, and a directcurrent source of constant voltage connected to said motor in polarityopposition to the current supplied by said tube to said motor, saidmotor being energized to rotate in one direction When the current fromsaid tube is greater than the current from said source, and beinenergized to rotate in the opposite direction when the current from saidtube is less than the current from said source.

5. A voltage stabilizing system for a radio frequency generator,comprising means for varying the voltage of the radio frequency outputcurrent of the generator; a reversible motor having an armature windingfor adjusting said voltage varying means; means for rectifying radiofrequency current from said generator; means utilizing the rectifiedcurrent for supplyin pulses of direct current the frequency of which isproportional to the value of the rectified current, to said armmaturewinding, and a direct current source of constant voltage connected tosaid winding in opposite polarity to said direct current pulses, saidmotor being energized to rotate in one direction when the average valueof the said pulses is greater than the direct current from said directcurrent source, and being energized to rotate in the opposite directionwhen the average value of said pulses is less than the current from saiddirect current source.

6. A voltage stabilizing system for a radio frequency generatorincluding an oscillator tube having a filament, comprising a source ofcur rent for said filament; means including a reversible motor having anarmature winding for adjusting the voltage supplied to said filament bysaid source; means for rectifying radio frequency current from saidgenerator; means utilizing the rectified current for supplying pulses ofdirect current the frequency of which is proportional to the value ofthe rectified current to said armature winding, and a direct currentsource of constant voltage connected to said winding in oppositepolarity to said direct current pulses, said motor being energized torotate in one direction when the average value of the same pulses isreater than the direct current from said direct current source, andbeing energized to rotate in the opposite direction when the averagevalue of said pulses is less than the current from said direct currentsource.

7. A voltage stabilizing system for a radio frequency generator,comprising means for varying the voltage of the radio frequency outputcurrent greater:

of; the generator; a reversible motor havlngan armature winding foradjusting said voltage varying means; a rectifier for rectifying radiofrequency current from said generator; means including which isproportional to the value of the rectified current; and adirectcurrentsource of constant voltage connected to 'said winding in oppositepolarity'to said direct currentpulses, said motor being energized torota-tein one direction when the average value of the said-pulses isgreater than the directcurrentfromsaid direct current source, and'beingenergized to rotate-in the opposite direction whenthe average value ofsaid pulses is less than the current from said direct current source.

8. A voltage stabilizing system for a radio frequency generatorincluding an oscillator tube having a filament, comprising a'sourceofcurrent for said filament; means including a reversible motor havingan armature winding for adjusting the voltage of thevcurrent supplied bysaid source to the filament; a rectifier for rectifying radio frequencycurrentfrom said generatorymeans including a gaseous electron tube forsupplying direct current to said winding; means utilizing the rectifiedcurrent from saidrectifier forcausing said tube to intermittentlyconductand tosupply-directcurrent pulses to said winding at a frequencywhich isproportional to the value of 'therectified 'current,and a direct currentsource of constant voltage connected to said winding in oppositepolarityto said direct current pulses, said motor being energized torotate in one direction when the average value of said pulses is greaterthan the direct-current from said direct currentsource, and beingenergized to rotate in the opposite direction when the average value ofsaid pulses is less than the current from said direct current source.

9."A voltage stabilizing system for a radio frequency generator,comprising means for varyinginthe voltage 0f the radio frequency outputcurrent ofl'thegenerator; a reversible motor having an armature' foradjusting said voltage varying means; a rectifier for rectifying radiofrequency current from said generator; means including'agaseous-electron tube for supplying direct current to said armaturewinding; means including a capacitor connected to said rectifier and'tosaidtube forbiasing said tube to inter- I in opposite polarity to saiddirect'current pulses;

said motor being energized to rotate in one direction when theaveragevalue of said" pulses is greater than the direct current fromsaiddirect current source, and being energized to rotate in theoppositedirection when the average value of said pulses is less than thecurrent from said direct current source.

10. Avoltage stabilizing system for a radio frequency generator,comprisingmeansfor varying the voltage of v the radio frequency outputcurrent of the generator; a reversible motor' havingan armaturewindingfor adjusting said voltage varyingmeans a -rectifier having ananode-for rectifying radio frequency-' current from said generator; acapacitor: having one side oonnected to saidanode a gaseous electrontubehaving a cathode; a grid and ananode; meansconnecting-"theother side ofsaid capacitor to said cathode; a powersupplysource for'saidtube, 'aresistor shunted across said source;-means connecting saidgrid and saidanode"of""said tube todifferent-points along said resistorj means forsupplying-direct current from said tube when it conducts to saidarmature winding, and

adirect current source of constant voltage connected-to saidarmaturewinding in opposite polarityto-the current from said-tube, saidmotorbeing energized to rotate in one direction-when the current fromthe said tube 'tosaid Winding is greater than the current from saiddirect current source to said winding, and being energized to rotateinthe opposite direction when the current from said tube to saidwinding-isless thanl the current from said direct current source :tosaid winding.

11. A voltage stabilizing'system for a radio frequency generatorincluding an oscillator tube havinga filament, comprising asource ofcurrent for said filament; means including a* reversible motor having anarmature winding for adjusting the voltage of the current supplied bysaid-source to said filament; arectifier-having an. anode.vforlrectifying radio frequencycurrent from. saidlgenerator; a capacitorhaving one side connected'to said anode; a.gaseous electron tubehaving acathode,a grid and an anode; means. connecting the-othersidezof saidcapacitor to said: cathode; a power supply source for said tube, aresistor shunted across said source; means lconnectin said gridandlsaidranode of saidltubetodiiferent points alongsaid resistor; means.for supplying direct current from said tube'when it conducts to saidarmature windingyand a direct current source of constantvoltage-connected to said armature windinguin opposite polarity to thecurrent from said tube,

said motorbein energized to rotate in one direction'when the currentfrom the said tube to said' current from said generator, and having acathode; a resistor connected to said cathode and toground; a gaseouselectron tube 'having a grid,- acathode and-an anode; a-capacitor hav--ingr one side connected to ground and having its other side connectedtosaid cathode of said gaseous tube; means includin a resistor con-'necting said other side of said capacitor to said anode of' said"rectifier tube; a power supply source" for said tube, a resistor shuntedacross said source, means connecting said grid and saidanode-of'saidtubeto different points along said resistor; meansfor'supplyingdirect current from said tube when it conducts to saidarmature winding, and a direct current source of constant voltageconnected to said armature winding in opposite polarity to the currentfrom said tube, said motor being energized to rotate in one directionwhen the current from the said tube to said winding is greater than thecurrent from said direct current source to said winding, and beinenergized to rotate in the opposite direction when the current from saidtube to said windin is less than the current from said direct currentsource to said winding.

13. A voltage stabilizing system for a radio frequency generatorincluding an oscillator tube having a filament, comprising a source ofcurrent for said filament; means including a reversible motor having anarmature winding for adjusting the voltage of the current supplied bysaid source to said filament; a rectifier tube having an anode connectedto receive radio frequency current from said generator, and having acathode, a resistor connected to said cathode and to ground; a gaseouselectron tube having a grid, a cathode and an anode; a capacitor havingone side connec.ed to ground and having its other side connected to saidcathode of said gaseous tube; means including a resistor connecting saidother side of said capacitor to said anode of said rectifier tube; apower supply source for said tube, a resistor shunted across saidsource; means connecting said grid and said anode of said tube todifferent points along said resistor; means for supplying direct currentfrom said tube when it conducts to said armature winding, and a directcurrent source of constant voltage connected to said armature winding inopposite polarity to the current from said tube, said motor beingenergized to rotate in one direction when the current from the said tubeto said winding is greater than the current from said direct currentsource to said winding, and being energized to rotate in the oppositedirection when the current from said tube to said winding is less thanthe current from said direct current source to said winding.

14. In combination a thermionic oscillation generator, an electricdischarge valve having principal electrodes and a control electrode,connections between said generator and said control electrode forvarying the conductivity of said valve in accordance with theoscillatory voltage of said generator, and connections between saidprincipal electrodes and said generator for varying the oscillatoryvoltage of said generator in dependence upon the variation of theconductivity of said valve.

15. In combination a thermionic oscillation generator, an electricdischarge valve having principal electrodes and a control electrode,connections between said generator and said control electrode forvarying the conductivity of said valve in accordance with theoscillatory voltage of said generator, and connections between saidprincipal electrodes and said generator for varying the oscillatoryvoltage of said generator in dependance upon the variation of theconductivity of said valve in a sense such as to tend to restoring saidoscillatory voltage to a magnitude from which it varies.

16. In combination a thermionic oscillation generator including a firstelectric discharge valve having a cathode to be heated; a secondelectric discharge valve having principal electrodes and a controlelectrode; connections between said generator and said control electrodefor varying the conductivity of said second valve in dependence upon thevariation in the oscillatory voltage of said generator; and connectionsbetween said principal electrodes and said cathode for varying thetemperature of said cathode in dependence upon the varying conductivityof said second valve.

17. In combination a thermionic oscillation generator including a firstelectric discharge valve having a cathode to be heated and an outputload circuit; a second electric discharge valve having principalelectrodes and a control electrode, said second valve being of thegaseous type; connections including a capacity coupling to said loadcircuit between said generator and said control electrode for varyingthe conductivity of said second valve in dependence upon the variationin the oscillatory voltage of said generator; and connections betweensaid principal electrodes and said cathode for varying the temperatureof said cathode in dependance upon the varying conductivity of saidsecond valve.

18. In combination a thermionic oscillation generator comprising a pairof push-pull connected electric discharge devices and an output tankcircuit, each of said discharge devices having a cathode to be heated, agaseous discharge device having principal electrodes and a controlelectrode, connections between said output tank circuit and said controlelectrode for varying the conductivity of said gaseous discharge devicein dependence upon the variation in the oscillatory output voltage ofsaid generator, and connections between said principal electrodes andeach of said cathodes for varying the temperature of said cathodes independence upon the varying conductivity of said gaseous dischargedevice.

RICHARD H. HAGOPIAN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,175,694 Jones, Jr Oct. 10, 19392,318,948 Koch May 11, 1943 2,415,799 Reifel et a1. Feb. 11, 19472,431,902 Albin Dec. 2, 1947 2,439,816 Marshall Apr. 20, 1948

